One form of sprung seat frame for a seat such as for use in a motor vehicle, as can be found in DE 30 42 604 C2, comprises a base plate which for example can be secured to the floor of a motor vehicle, and a seat plate which can receive for example the seat upholstery. Disposed between the seat and base plates is a scissors-type frame assembly comprising first and second levers which are pivotally connected together in their central region in a crossed or scissor-like configuration. The levers are each connected by respective end portions to the base plate and the seat plate respectively, one end being pivotally connected to the respective plate and the other end being connected to the respective plate in such a way as to be linearly movable in relation thereto on a suitable guide means provided on the respective plate. A springing system including a compression spring is operatively disposed between the lever assembly and the base plate, to provide for springing of the seat frame.
As a result of the small amount of space available for accommodating the compression spring between the lever assembly and the base plate, such a seat frame structure can use only a relatively compact spring. However a compact spring of that kind has a high spring rate, thus generally resulting in a seat frame which has hard springing characteristics.
In terms of a springing system, reference may be made to DE 35 17 345 C2 disclosing a springing arrangement comprising a coil tension spring and a member which acts thereon. The non-linear dependency of the spring force on the distance covered by said member is not only dependent on the spring rate of the coil spring but is also adjustable by said member itself. Furthermore, in general terms of springing, reference may be made to German patent specification No 943 171 disclosing progressive springing for rail vehicles by means of a spring band composed of a plurality of spring wires or thin-gauge blade members.